1. Field of the Invention
This invention relates to a sheet feeding apparatus in an image forming apparatus such as a photocopier, a printer, or the like or in an image reading apparatus for reading image information formed on sheets.
2. Description of Related Art
FIG. 14 shows a schematic cross section of a sheet feeding apparatus capable of successively feeding sheets in use of an intermediate plate 100, a feeding roller 101, and a separating roller 102 and a Schematic cross section of a separation guide 103. The separation guide 103 formed in having a uniform cross section in a sheet width direction near the separating roller 102 is provided at a certain distance away from a separation nipping portion as a sheet nipping portion at which the feeding roller 101 and the separating roller 102 rotating with a prescribed torque in a direction returning the sheet with the feeding roller 101. A hitting plate 103 extending approximately vertically with respect to the intermediate plate 100 so that the sheet front end stacked on the intermediate plate 100 hits to the plate 103 while the intermediate plate 100 is disengaged is disposed on an upstream side in the sheet feeding direction of the separation guide 103 with respect to the separation nipping portion.
The separation guide 103 has an opening 103c to project the separating roller 102 from a guide surface 103b to sandwich the sheet with the feeding roller 101 at prescribe pressure. A pulling roller 104 is formed on a downstream side in the sheet conveyance direction of the feeding roller 101, thereby further feeding in the downstream direction the sheet fed from the feeding roller 101.
In feeding operation, where the intermediate plate 100 moves in a direction contacting with the feeding roller 101, the sheets stacked on the intermediate plate 100 come in contact with the feeding roller 101, thereby conveying the front ends of the sheets sent by the feeding roller 101 to the separation nipping portion along the separation guide 103.
The sheets are conveyed toward the pulling roller 104, and when the sheets other than the topmost sheet are sent to the separation nipping portion, the separating roller 102 rotating with a prescribed returning torque reverses the sheets in the direction of the intermediate plate 100 to prevent the plural sheets from being fed at a time. Where a single sheet is nipped at the separation nipping portion, the separating roller 102 rotates in the conveyance direction according to the rotation force of the feeding roller 101.
In the sheet feeding apparatus thus structured, however, if sheets having a high rigidity and a large frictional coefficient between the sheets are fed, sheets next to the topmost and below may enter in the nipping portion when the sheets enter in the separation nipping portion, and the sheet front end hits the outer peripheral surface of the separating roller in the center direction (or normal direction) of the separating roller, giving the separating roller 102 force in a direction of arrow F, thereby pushing down the separating roller 102 to isolate from the feeding roller 101.
Where the separating roller 102 separates from the feeding roller 101 and where the front ends of the sheets next to the topmost and below hit the separating roller 102, the nipping force for nipping the sheets with the feeding roller 101 and the separating roller 102, or separation pressure that the separating roller 102 contacts in pressure with the feeding roller 101 is greatly reduced. Where the separation pressure is reduced, the separating roller 102 cannot rotate in following the rotation of the feeding roller 101 and the conveyance of the topmost sheet and may rotate in the returning direction. The feeding roller 101 thereby cannot feed the sheet further, so that the sheets cannot be conveyed to pulling roller 104.
Where the sheets are conveyed from the separation nipping portion, if the sheet has a high rigidity, the sheets are conveyed in a state that the separating roller 102 are pushed down in a direction separating from the feeding roller 101. That is, the sheets are conveyed in the direction as sinking down in a direction of arrow F. The separation guide 103 has the opening 103c only for the roller width of the separating roller 102, so that the sunken sheet front end may hit an end 103d of the opening 103c of the separation guide 103 and may cause paper jamming.
This invention is conceived to solve the above problems. It is an object of the invention to provide a sheet feeding apparatus capable of stably feeding sheets without any conveyance failure even where sheets having a high rigidity or having a large frictional coefficient between the sheets are conveyed.
A representative structure of the invention to accomplish the above objects includes sheet supporting means movable for supporting a sheet or sheets; a feeding rotary member in contact with the sheet supported by the sheet supporting means to feed out the sheet upon rotation of the feeding rotary member; and a separating rotary member forming a contact portion in contact with the feeding rotary member and being rotatable in a direction returning the sheet to separate the sheet fed out of the feeding rotary member, wherein the sheet supporting means, the feeding rotary member, and the separating rotary member are so disposed that an angle formed on a side facing to the feeding rotary member by intersecting a tangential line of the feeding rotary member at a contacting position between the feeding rotary member and the sheet with a tangential line at the contact portion is an obtuse angle, and further includes a conveyance guiding means disposed on a side of the separating rotary member with respect to the contact portion for guiding the sheet fed to the feeding rotary member to the contact portion, the conveyance guiding means having a projection guiding means for projecting the contact portion on an upstream side in the sheet conveyance direction of the contact portion more toward the side of the feeding rotary member than a guide surface of the contact portion.